This invention relates to golf balls, and, more particularly, to a golf ball which includes a lattice structure between the core and the cover.
Since the advent of the solid two-piece ball in the 1970""s, different companies have tried to manufacture a solid ball with good spin characteristics, good distance, and good feel. Generally, with just a solid rubber core and a thermoplastic cover to work with, a golf ball developer can achieve two of these three attributes to one degree or another. For example, a designer can achieve good spin and distance, but at the detriment of feel. Likewise, a designer can achieve good feel and spin, but only with a loss of distance.
One method companies have used to overcome this shortfall of solid balls is the employment of double covers. Golf balls have been proposed which have two covers, one formed from a soft resin, the other formed from a hard resin. By using combinations of these different covers, some of the design constraints of the two-piece solid ball can be overcome. However, other disadvantages remain. For instance, if a designer uses a soft inner cover and hard outer cover, the ball still lacks adequate spin for certain types of products. If a designer uses a hard inner cover, and a soft outer cover, the product is essentially a distance two-piece ball with an outer cover over it.
Generally, the manufacture of these multi-covered balls encounters one of several problems. First, if both covers are thick enough to be injection molded, the total combined thickness of the two covers over the core is too large to achieve adequate feel, spin, and distance. If this total thickness is reduced, one of the covers must be thinned, and thus must either be compression molded or some type of manufacturing process, such as centerless grinding of the inner layer, must take place. This increases cost and complexity.
Some golf balls include a mantle layer between the core and the cover. The mantle layer may be formed from materials which are conventionally used in covers, for example, ionomer resins, or from materials which are conventionally used in cores, for example, polybutadiene. A mantle layer presents the same difficulties as an inner cover layer.
It is not essential that a full mantle or inner layer be molded on the core, rather just a substructure is sufficient. This substructure should accomplish several important objectives. First, it should provide adequate support for the typically solid rubber core during impact. It should hold the core substantially spherical in shape for maximum energy transfer during and after impact. Secondly, it should not require additional total cover thickness to achieve the desired initial velocity or distance. Thirdly, the substructure should either not, or only slightly, affect the feel and playability of the ball as detected by the golfer.
The invention provides this substructure as a lattice structure, which covers only portions of the core and leaves other portions of the core exposed. The lattice would be structural enough to provide the support required by the core during impact, but innocuous enough to not cause detriment to the playability aspects of the ball.
This lattice could come in any form and preferably comprises a series of bands about the core. In order to obtain some sort of symmetry about the sphere, the lattice may replicate one of the Platonic or Archimedean solids which is projected onto the surface of a sphere. The bands or lattice legs then occupy the same great circle paths as created by the boundary of the polyhedra of the solid. For example, for an octahedron, the lattice would entail three bands circumnavigating the ball, each at right angles from each other. Other solids which could be utilized include, but are not limited to, the cuboctahedron, the icosahedron, and the icosadodecahedron.
The lattice can be used with a homogenous or multi-layered core and with a homogeneous or multi-layered cover or combinations thereof.